Magnetic sound record



Jan. 8, 1952 AN HAL 2,581,765

MAGNETIC SOUND RECORD Filed April 20, 1948 INVENTORS THEODORE. N, MANN THEODORE c. MANN BY ATTORNEY Patented Jan. 8, 1952 MAGNETIC SOUND RECORD Theodore H. Mann and Theodore G. Mann,'Los

Angeles, Calif., assignors to Sound Engineering Hollywood, Calif., a partnership Application April 20, 1948, Serial No. 22,078

This invention relates to magnetic sound recording and in particular to a form for the face of the record base upon which a magnetic recording may be recorded and reproduced without the use of any driving mechanism for moving the head across the face.

Magnetic recording has many advantages over other recording methods but its general use has been restricted heretofore by the fact that magnetic recording materials in the usual form such as wire or tape or plain surfaced discs or cylinders require specialized driving mechanism to advance the recording or playing head on the spiral or helix. Heretofore, it has not been possible to use in connection with magnetic recordings, the existing recording and play-back equipment which is commonly available in phonograph record players because in these the pointed stylus follows a pre-formed spiral or helical groove and does not require a cross feeding mechanism such as that required in magnetic recordings on, for example, plain discs.

The principal object of this invention is to provide a surface on a disk or cylinder adapted for magnetic recording which can be recorded or played by utilizing available phonograph equipment upon which there has been substituted a magnetic type recording or play-back head.

In accordance with this invention, a magnetic recording base is made up in disk or cylinder form similar in size to ordinary phonograph records of these types and is provided with aspiral groove of special saw toothed cross-sectional shape, which is engaged by the contacting foot of the translating magnetic head, which is shaped on one side to ride in the bottom of the groove and against the steeper wall of the groove, while the other side of the foot passes closely adjacent the longer and flatter wall of the groove surface, on which flatter wall the magnetic record is impressed.

The recording base may be made in a number of ways depending on the characteristics of the particular structural material used, the standard of quality desired in the recording and reproduction and in the type of service for which the recording is to be used.

The invention will be described in relation to a grooved disk type recording base, although any form of continuous curved groove type bases such as disks or cylinders may also be used, reference being made to the accompanying drawings in which:

Fig. 1 is an enlarged cross-sectional view showing the saw toothed grooves made in a uniform base material;

- 6 Claims. (Cl. 274-414) Fig. 2 is an enlarged cross-sectional view showing the saw toothed shaped grooves, the flatter surfaces only having a relatively thin layer of magnetic recording material thereon;

Fig. 3 is a side elevational view of a typical recording or translating magnetic head; and

Fig. 4 is a cross-sectional view showing the contacting foot of the recording head in contact with one saw-toothed groove of the record base.-

Figure 1 shows a record base of suitable magnetic material throughout in which the spiral saw-toothed grooves are formed either in the pressing of the blanks or by cutting the grooves previous to making the magnetic recording. In Figure 2 is shown a form of my invention in which the record body may be made of any suitable material such as synthetic plastic, glass, ceramic or non-magnetic metals, the flatter wall surface of the saw-toothed groove being coated with a layer l2 of suitable magnetic recording material deposited on or otherwise aifixed to the flatter groove face. In this form, the spiral groove with saw-toothed cross-section is pre-formed on the flat face of the body of the material by any suitable process such as by pressing or by cutting.

One method of forming a record body of the type shown in Figure 2 is to pre-form saw-toothed shaped grooves in a non-magnetizable base; then fill the grooves with a magnetizable coating material, followed by recutting the grooves to leave the magnetizable material only on the flatter wall of the groove. Another method of preparing the record base consists in forming a homogeneous dispersion of magnetic material in a resinous binding and dispersing material such as styrene, vinylite and the like, and then pressing the body in forming dies which impress the sawtoothed grooves in the surface or surfaces. One composition which has been found to be satisfactory for this purpose consists of about parts by weight of ferric oxide powder, 30 parts by weight of styrene, and .5 part by weight of lead stearate.

By using a saw-toothed shaped groove on whose flatter wall the magnetic recording is made, the magnetic head is guided along the pre-formed spiral by the foot 15 which rides in the bottom I6 of the groove and also on the steeper wall [1, which may or may not be covered with magnetic recording material. The foot of the recorder or translating magnet is guided by the steeper wall I! of the spiral groove so that the translating magnet is carried over the entire length of the spiral groove without mechanical transverse spiral guiding mechanisms. In other words, the ordinary stylus supporting arm of a phonograph which is arranged by suitable pivoted joints to follow a spiral groove by moving in an arc across the disk as the stylus follows the spiral groove may be utilized for supporting the magnetic head, with the specially shaped foot l5 following the bottom of the groove, and with side thrust against thesteeper walls |:-1-. Any suitable ty e of magnetic recordingxo'r. translating device having a suitably shaped foot to pass along the saw-toothed shaped grooves;- may be used. An illustrative translating magnet is shown in Figure 3, with a detailed cross sec tional View of the foot shown in-li iguresfzcedf'said groove having the lesser inclination The magnetizable compositionifor the record- '7 ing base, either for the single layer record: of

Figure 1, or for the double layer form of Figure 2,

may consist of any suitable non-magneticmate= rial such as cellulose acetate, vinyl-type p'lastics;

etc., in which there is distributed iron or ironoxideparticlesbf a kind and in suitable concentration to be effective as a magnetic. recording, material, followingthe well 'known practices of this art. v g

, The advantages oi'our invention willibe apparent. I he useofa pre-formed 'saw-toothedgroove,

one wall of whichserves as. the magnetic recording surface andItheother wallof which acts to guide thefrnagneticlliead in. a spiral or helical path, gives a maxirnum length of. recording surface. on. a given sizeddisk. or cylinden sihce no space is requiredlfor land's" between the grooves.

When a recordbaseoflthetype shown in Figure 2.is used,the=undesirediecho effect is avoided; Groove echo is the resultof. spreading the ma netization beyondthe desired .boundaries andthis is minimized-in the saw-toothed groove design because the edges of the magnetizable. coating are spaced a maximumdistanceaway from those of the adjoiningrgroove edges- The-use. of the sawtoothed grooved records. facilitates. the conversion-of the ordinary. phonograph player to use magnetic recordings and p1ayings,, because no cross-feeding mechanism is required, and the supporting arm of theusual mechanical stylus from-the horizontal being adapted to receive magnetic sound recordings and the adjacent convolution's1of said continuous curved groove being contiguous at acommon edge.

4". A magnetic sound record comprising a continuoussolid record base having thereon a continuous curved groove of non-equilateral sawtoothcross-sectional shape, at leastthe wall surface of said. groove having the lesser inclination.

from the. horizontal being. provided with a coat ing of magnetic recording. material and the adjacent convolutions oflsaid continuous curved groove being contiguous at acommon edge.

5. A. magnetic sound record comprising. a homogeneous continuoussolid record. base of magnetic. recording material,-'sai'cl'-. b'asei having. thereona continuous curved groove oinonsequil'ateral' saw-tooth. cross-sectional.shape,,.one wall surface of said groove being adaptedlto receive magnetic sound. recordings andthe adjacent convolutions of said. continuouscurvedl groove being. contig uous at a common edge.

6.' A magneticv sound record'. comprising. a homogeneous continuousfs'olld' record base of maginetic recording.materiaLsaidbase having thereon a continuous curved' groove of non-equilateral saw-tooth cross-sectional.shape, the wall surface of'said' groovehavingthe lesser inclination from the horizontal being adapted t'o-receive magnetic sound recordings. and the. adiacent convolutions of said. continuous. curved. groove being contiguous. at a common edge."

. TI-IEODURE H. MANN. THEODOREG'. MANNZ I REFER-ENCES'.CITED The following. references. are of recordcin the file of: this: patent:

um rsn STATES rATENms 

